1. Field of the Invention
This invention relates to a copolyester and a gas-barrier property imparting agent, and more specifically, to a copolyester having excellent gas-barrier property and surface properties and a high glass transition temperature and a gas-barrier property imparting agent composed of the copolyester.
The invention also relates to a polyester composition and a film, a preform and a container composed of the polyester composition, and more specifically, to a polyester composition having excellent gas-barrier property, surface properties and transparency and comprising (A) polyethylene terephthalate and (B) the aforesaid copolyester, and to a film, a preform and a container composed of the polyester composition.
Furthermore, this invention relates to a polyester laminated structure, and its use, and more specifically, to a polyester laminated structure having excellent moldability, mechanical properties and composed of (C) a polyalkylene terephthalate layer and (D) a copolyester layer composed of the aforesaid copolyester or a polyester composition, and to its use.
2. Description of the Prior Art
Glass has widely been used as a material for containers for holding various articles, for example seasonings, oils, wines and liquors, beer, soft drinks including carbonated drinks, cosmetics, and detergents. Glass containers have excellent gas-barrier property, but their cost of production is high. It is the usual practice therefore to recover the used empty containers and recycle them for use. The glass containers, however, are heavy and involve high transportation expenses. Moreover, they are susceptible to breakage and inconvenient to handle.
To solve this problem, the glass containers have been superseded by various plastic containers, and various plastic materials are used according to the kind of articles to be held and the purpose of use. Polyethylene terephthalate (PET) has excellent thermal resistance, impact strength, gas-barrier property and transparency, and is used as a material for containers used to hold seasonings, refreshing drinks, detergents and cosmetics. In the case of containers for beer and carbonated drinks which most rigorously require gas-barrier property, polyethylene terephthalate is still not entirely satisfactory. To use polyethylene terephthalate for such containers, it is necessary to improve gas-barrier property by increasing the thickness of the containers.
Polyester containers have shown an increasing demand, but to expand their use further, it is strongly desired to develop polyesters having excellent gas-barrier property and melt-moldability.
Japanese Laid-Open Patent Publication No. 84866/1981 discloses a multilayer container having a thin wall portion in which the outermost layer and the innermost layer are composed of a polyester having ethylene terephthalate as main recurring units, an interlayer is composed of a polyamide obtained by reacting a dibasic acid component and a diamine component, the diamine component being m-xylylenediamine or a mixture of it with p-xylylenediamine, and the resin constituting the thin wall portion is oriented in at least one direction. This patent document describes that the above container has excellent oxygen gas-barrier property while retaining the excellent dynamical properties, transparency and chemical resistance of the polyester.
Japanese Laid-Open Patent Publication No. 183248/1983 discloses a biaxially stretched blow molded bottle in which both inside and outside surface layers are composed of polyethylene terephthalate and a layer intermediate between them is composed of a mixture of polyethylene terephthalate and a xylylene group-containing polyamide.
Japanese Laid-Open Patent Publication No. 64624/1984 discloses a polyalkylene isophthalate such as polyethylene isophthalate and its copolymer, and a packaging material having good gas-barrier property with respect to oxygen and carbon dioxide gas which is molded from them.
Japanese Laid-Open Patent Publication No. 87049/1984 discloses a multilayer packaging material composed of a layer of a polyalkylene isophthalate or its copolymer and a layer of a polyalkylene terephthalate such as polyethylene terephthalate or its copolymer, and a molded article such as a bottle formed from it.
Japanese Laid-Open Patent Publication No. 64658/1984 proposes a method of blending polyethylene isophthalate and polyethylene terephthalate.
However, the polyethylene isophthalates described in the above-cited patent documents contains high-melting oligomers, and these oligomers adversely affect the physical properties of the resulting molded articles.
To improve the gas-barrier property of PET, a copolyester was proposed which is prepared by copolymerizing isophthalic acid as a dicarboxylic acid component and ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene as a dihydroxy compound component (see Japanese Laid-Open Patent Publication No. 167617/1983).
If an article such as a container is molded from a polyester resin containing moisture, hydrolysis takes place and the mechanical properties of the molded article are degraded. It is necessary therefore to dry the polyester resin before molding. However, since an isophthalate-type copolyester containing a large amount of isophthalic acid as the dicarboxylic acid component has a lower crystallinity and glass transition temperature (Tg) than a terephthalate-type copolyester, it can be dried only at low temperatures. Accordingly, to obtain an isophthalate-type polyester having a low water content, long periods of time are required for its drying. If the isophthalate copolyester is dried at temperatures higher than the glass transition temperature, the copolyester will melt-adhere to itself.
Usually, polyethylene terephthalate is dried at a temperature of 110.degree. C. to 160.degree. C. If the polyethylene terephthalate dried at the above temperatures and the isophthalate-type copolyester dried at lower temperatures are dry-blended immediately after drying, the isophthalate-type copolyester will be heated to a temperature higher than the glass transition temperature by the polyethylene terephthalate which is still at a considerably high resin temperature. Consequently, the pelletized isophthalate-type copolyester will get out of shape or the copolyester pellets melt-adhere to one another. Consequently, it is difficult to mix them uniformly.
For this reason, it has been desired to develop an isophthalate-type copolyester having a high glass transition temperature (Tg) and excellent thermal resistance.
An isophthalate-type copolyester having copolymerized therein bis(4-beta-hydroxyethoxyphenyl)sulfone was proposed as a copolyester having a high glass transition temperature (Tg) (see Japanese Laid-Open Patent Publication No. 167617/1983).
The use of bis(4-beta-hydroxyethoxyphenyl)sulfone makes the isophthalate-type copolyester slightly higher in glass transition temperature (Tg), but its Tg elevating effect is not sufficient. In addition, if its gas-barrier property is degraded, or the copolyester is colored or the monomeric components bleed out, the polyester is undesirable in view of food sanitation.